Experimental observations of bifurcated power decay lengths in the near Scrape-Off Layer of ST40 High Field Spherical Tokamak
The scrape-off layer parallel heat flux decay lengths measured at ST40, a high field, low aspect ratio spherical tokamak, have been observed to bifurcate into two groups. The wide group follows established H-mode scalings (ranging between 2 to 8 mm) while the narrow group falls up to 10 times below these scalings (between 0.2 and 0.8 mm), being comparable to the ion total Larmor radius rather than the ion poloidal Larmor radius. The heat flux profiles of the latter group can only be described by a multi-exponential function, rather than the single exponential function convoluted with a Gaussian. The onset of the narrow scrape-off layer width is observed to be associated with suppressed magnetic fluctuations, suggesting reduced electromagnetic turbulence levels in the SOL. • The ST40 tokamak achieved double null diverted configuration, with divertor diagnostics. • A database of Scrape-off Layer width measurements has been established. • Scrape-off Layers widths up to 10 times below scaling were discovered. • The onset of very narrow Scrape-off Layer widths was correlated with reduced electromagnetic fluctuations.
Authors
- Martin P. Robinson (ORCID: https://orcid.org/0000-0003-1767-5541)
- M. Sertoli (ORCID: https://orcid.org/0000-0003-1528-6307)
- Travis Gray (ORCID: https://orcid.org/0000-0001-8220-8195)
- P.F. Buxton (ORCID: https://orcid.org/0000-0002-0349-0434)
- X. Zhang (ORCID: https://orcid.org/0000-0003-3775-5821)
- Steven McNamara (ORCID: https://orcid.org/0000-0002-0477-5247)
- Salomon Janhunen (ORCID: https://orcid.org/0000-0002-8022-0825)
- E. O. Vekshina (ORCID: https://orcid.org/0000-0001-9771-5579)
- Nicolas Lopez (ORCID: https://orcid.org/0000-0001-5566-3731)
- C. Marsden
- M. Moscheni (ORCID: https://orcid.org/0000-0002-6355-7274)
- Hazel Lowe (ORCID: https://orcid.org/0000-0002-9085-1073)
- A. Scarabosio (ORCID: https://orcid.org/0000-0002-7372-6975)
- F. Romanelli (ORCID: https://orcid.org/0000-0001-9778-1090)
- A. Rengle (ORCID: https://orcid.org/0009-0001-9037-1125)
- E. Maartensson (ORCID: https://orcid.org/0009-0000-7289-8516)
- T. O’Gorman (ORCID: https://orcid.org/0009-0006-8803-015X)
Institutions
- Oak Ridge National Laboratory (US)
- Los Alamos National Laboratory (US)
- University of Oxford (GB)
- Tokamak Energy (United Kingdom) (GB)
- Scientific Consulting Group (US)
- LINKS Foundation (IT)
Publication Details
- Journal
- Nuclear Materials and Energy
- Published
- 2024-10-22
- DOI
- https://doi.org/10.1016/j.nme.2024.101772
- Citations
- 8
- Primary Topic
- Magnetic confinement fusion research
- Type
- article
- Field-Weighted Citation Impact
- 5.28
Funders
- Fusion Energy Sciences